1. Field of the Invention
This invention relates to a laser recording monitoring system for monitoring a record on a heat-mode recording medium recorded by a modulated laser beam.
2. Description of the Prior Art
There has been known a recording method in which a laser beam modulated in accordance with data signals is caused to scan a heat-mode recording medium. The heat-mode recording medium includes a recording layer the optical density of which is normally high and is reduced significantly when the recording layer is exposed to a high energy beam such as a laser beam. For example, there has been known such a recording medium having a recording layer the exposed part of which is fused or evaporated by the heat produced by the laser beam to permit light to pass therethrough. The heat-mode recording material typically comprises a transparent base film of glass, polyethylene terephthalate or the like, and a recording layer of high optical density containing therein metal, semimetal or the like. The heat-mode recording medium may further include a protecting layer, a light absorbing layer, a reflection preventing layer and a primer layer. These layers are well known in the art and are disclosed in detail in Japanese Patent Application Laid Open Nos. 51(1976)-78236, 52(1977)-20821 and 53(1978)-83617.
Information is recorded on the heat-mode recording medium as a pattern of parts made to permit light passing therethrough.
When the head-mode recording medium has a pin hole or foreign materials in or on the recording layer thereof, incorrect information may be recorded on the recording medium since the pin hole permits light to pass therethrough even if the part of the recording layer is not exposed to the recording laser beam and the foreign material prevents the part of the recording layer from being fused or evaporated by the heat produced by the laser beam. The record on the heat-mode recording medium cannot be corrected. Thus, a monitoring system for monitoring the record on the heat-mode recording medium becomes necessary.
Japanese Patent Application Laid Open No. 51(1976)-109851 discloses a system for accomplishing such monitoring. In this system, a laser beam for monitoring is caused to scan along with the modulated laser beam for recording so that both the beams simultaneously impinge on one and the same point of the recording medium. The laser beam for monitoring is not modulated and has a wave length different from that of the modulated laser beam for recording. The monitoring laser beam component is extracted from the reflected light and is converted into electric signals for monitoring. This system inherently involves use of an additional laser source and additional optical systems, thereby making the overall laser recording system more complicated, larger and more expensive.